1. Field of the Invention
The present invention relates to an in-core nuclear-measuring apparatus of a reactor and, more particularly, to a passage selector acting for selectively switching a passage selecting guide tube through which a detector cable goes with respect to a predetermined number of detector passages in the in-core nuclear-measuring apparatus.
2. Description of the Related Art
To measure a neutron flux to be discharged from fuel in a reactor core, the nuclear-measuring facilities for nuclear power plants are generally provided with a passage selector in which a cable equipped with a neutron detector at the leading end is selectively inserted into a plurality of detector passages. Although varied in number depending on its capacity, a reactor is provided with multiple detector passages, and the neutron detector is selectively inserted into these detector passages using the above-mentioned passage selector, thereby enabling to efficiently perform a remote detection of a neutron flux with small numbers of equipments. The construction of nuclear-measuring facilities of a reactor is described in detail, for example, in the Japanese Patent Publication (unexamined) No. 195572/2005.
The conventional passage selector is of a system in which by a turning force of a drive motor, a passage selecting guide tube is brought in rotation directly through an index device of various cam mechanisms. As the index mechanism of the above-mentioned cam mechanism, for example, a known roller gear cam mechanism, parallel cam mechanism, and Geneva mechanism can be employed. Furthermore, as the mechanism for positioning the passage selecting guide tube in rotation at an arbitrary detector passage, a mechanism that is referred to as a click stopper system, in which a hard sphere is pressed onto a rotary wheel by a spring force, is generally employed.
FIG. 5 is a view illustrating a schematic construction of a passage selector formed in the above-mentioned click-stopper system. In the drawing, reference numeral 1 designates a housing, numeral 2 designates a central rotating shaft, and numerals 3 and 4 designate disks that are provided at both ends of the above-mentioned housing 1 and supported by a fixed rod 15. Numeral 5 designates a passage selecting guide tube that comes in the housing 1 from the center of the above-mentioned disk 3, and going through an internal part of the above-mentioned central rotating shaft 2, comes out of the central rotating shaft 2 on the way, to be connected to the disk 4. In the internal part of this guide tube, a cable (not illustrated), to the leading end of which a neutron detector (not illustrated) is attached, is inserted to go through.
Numeral 6 designates a drive motor equipped with a reduction gear, which is directly connected to the shaft of an electromagnetic clutch 7 and fixed to the disk 3. Numeral 8 designates a first gear that is attached to the electromagnetic clutch 7, and meshes with a second gear 9 that is attached to the above-mentioned central rotating shaft 2. That is, these components form an index device directly performing a rotation index of the central rotating shaft 2 by gear ratio setting between the above-mentioned first gear 8 and second gear 9 with the rotation of the drive motor 6. The above-mentioned passage selecting guide tube 5 rotates by the same angle as that of the above-mentioned central rotating shaft 2, so that the above-mentioned passage selecting guide tube 5 is brought in rotation by a predetermined angle having been indexed by means of this index device to select a predetermined passage.
The second gear 9 is provided with a cam 10 causing a passage selecting switch 11 to operate. When this cam 10 causes a predetermined passage selecting switch 11 to operate, the power from the drive motor 6 is to be shut off (for example, refer to the Japanese Patent Publication (unexamined) No. 202696, 1989). Furthermore, the central rotating shaft 2 is disconnected due to that the power from the electromagnetic clutch 7 is shut off. In addition, the above-mentioned shaft 2, which otherwise passes by an inertial force of a wheel 12 is made to mechanically stop owing to that a click stopper 14 is pressed onto a dish-shaped groove 13 that is provided in the wheel 12. The click stopper 14, as described above, is constructed so that a hard sphere is pressed by a spring onto the wheel 12 going to rotate, which is the reason of being referred to as a click stopper system.